The present invention relates to compositions for the treatment of lead-based and lead-containing surface coatings or soil for the purpose of rendering said surface coatings or soil non-hazardous to humans. Specifically, the compositions are useful for the removal of lead-based paints from interior and exterior surfaces of a structure and for the treatment of lead-contaminated soil.
Lead-based coatings, for example, lead-based paint, may contain such compounds as lead chromate, lead molybdate, lead sulfate, lead borate, lead carbonate, lead monoxide, lead tetroxide, lead vanadate and lead antimonate. Soil surrounding public, private or Indian housing and structures of business may contain tetraethyl lead and perhaps other lead compounds.
Title X--Residential Lead-based Paint Hazard Reduction Act of 1992 defines by amendment to the Toxic Substances Control Act "lead-based paint" as paint on surfaces with lead in excess of 1.0 mg/cm.sup.2 as measured by a spectrum analyzer or direct reading x-ray fluorescence (XRF) detector, or 0.5 percent by weight. The XRF threshold had been established in the 1988 amendment to the Lead-based Paint Poison Prevention Act and remains unchanged. Title X's explicit standard of 0.5 percent by weight focuses attention and resources on surfaces with high levels of lead.
Title X also defines "lead-based paint hazard" as any condition that causes exposure to lead sufficient to cause adverse human health effects and it cites six situations which are:
Deteriorated lead-based paint such as any exterior or interior lead-based paint that is peeling, chipping, chalking or cracking, or is located on any surface or fixture that is damaged or deteriorated.
Lead-based paint on any "friction surface", an interior or exterior surface subject to abrasion or friction, such as painted floors.
Lead-based paint on any "impact surface", an interior or exterior surface subject to damage by repeated impacts such as parts of door frames.
Lead-based paint on any "accessible surface", an interior or exterior surface accessible to a young child to mouth or chew, such as a window sill.
"Lead-contaminated dust", surface dust in residential dwellings that contain an area or mass concentration of lead in excess of the standard to be established by the Environmental Protection Agency.
"Lead-contaminated soil", bare soil on residential property that contains lead in excess of the standard to be established by the Environmental Protection Agency.
Title X also defines "abatement" as any set of measures designed to permanently eliminate lead-based paint hazards in accordance with standards established by appropriate Federal agencies. Such abatement includes:
(A) the removal of lead-based paint and lead-contaminated dust, the permanent containment or encapsulation of lead-based paint, the replacement of lead-painted surfaces or fixture and the removal or covering of lead-contaminated soil; and PA1 (B) all preparation, clean-up, disposal and postabatement clearance testing activities associated with such measures.
Present state-of-the-art procedures for removing lead-based paint have serious disadvantages. The procedure described in U.S. Pat. No. 4,426,250 uses very caustic chemicals such as hydroxides of sodium, potassium, calcium and magnesium. A paste containing such chemicals is applied to the painted surface and is then covered with a fabric during at least part of the treatment period. The method is time consuming and relatively hazardous.
In recent years, the most commonly used paint stripping compositions have contained halogenated hydrocarbon chemicals, such as methylene chloride. Since such chemicals are suspected to be carcinogenic, there have been many attempts to replace them with combinations of other organic chemicals. U.S. Pat. No. 5,089,164 is one reference which describes paint stripping compositions which contain among other organic constituents a significant amount of N-methyl-pyrrolidone. It is our understanding that in the presence of water these compositions have significantly lower stripping rates than compositions containing methylene chloride and that organic stripping agents are not easily washed from the stripped surface.
Some stripping compositions have contained peroxides such as those in U.S. Pat. No. 3,355,385. These compositions, however, contain very volatile and flammable solvents which render the life of the composition as a stripping agent very short. U.S. Pat. No. 5,215,675 combines the use of hydrogen peroxide with water soluble esters in aqueous stripping compositions to eliminate such problems.
All of the above stripping compositions contain organic solvents and stripping agents which are not easily washed from the treated surface. Also, none of these references indicate that the compositions are useful for the stripping of lead-based paints.
Treatment of lead in soil has been limited in the prior art to immobilizing the lead by converting lead containing compounds to non-leachable forms. Examples of such immobilization are shown in U.S. Pat. No. 5,162,600, U.S. Pat. No. 5,202,033 and U.S. Pat. No. 5,234,485.
It is an object of this invention to provide an effective aqueous based composition for the abatement of lead whether it be in lead-based paint or in surface soils.